Various kinds of sound absorbers are used in various industries including automobiles, aircraft, buildings and the like in order to absorb sounds. The sound absorbers protect against undesired or harmful sounds based on an undesired frequency region in a given environment.
In particular, although porous materials are unsuitable for absorbing low frequency sounds, the porous materials are used for absorption of high frequency sounds due to demand for a considerable material thickness.
Among porous materials, for example, non-woven fabrics are produced by melt-blowing. Sound absorption capabilities of the non-woven fabrics are attributed to a porous sound absorption principle formed by micro fibers constituting the non-woven fabrics. However, porous sound absorption is advantageous in sound absorption in a high frequency band, but has a drawback of poor sound absorption in mid and low frequency bands. Thus, there is need for non-woven fabrics capable of providing good sound absorption capabilities even in mid and low frequency bands.
In the related art, Korean Patent Publication No. 2011-4418 A (publication date: Jan. 13, 2011) discloses a multilayer sound absorbing sheet, which includes a film layer having fine through-bores and openings and a fibrous material layer disposed on the film layer and thus has an improved coefficient of sound absorption in a frequency band of 1000 Hz or more.